Automated testing systems for integrated circuit devices are well known to those skilled in the art. Such systems may be used to test for a number of different types of faults. One common fault of interest for testing is the so called “stuck-at” fault in which the output of a logic circuit is persistently stuck in a certain logic state regardless of change in input. It is also important to be able to test for faults in response to tests conducted at system speeds (referred to in the art at “at-speed” fault detection). Stuck-at and at-speed testing is commonly performed with the use of automated test equipment (ATE).
Logic built-in self-test (LBIST) technology is well known in the art for testing the operation of integrated circuits. One advantage of LBIST is that the integrated circuit is functioning to test itself. This is especially important in connection with integrated circuits used in safety applications. Integrated circuits designed for military, medical and automotive implementations, for example, are common users of LBIST technology. LBIST is typically provided for testing random logic within the integrated circuit. A pseudo-random pattern generator (PRPG) operates to generate input test patterns that are applied to an internal scan chain. A multiple input signature register (MISR) collects the response of the device to the input test patterns. In the event the MISR output differs from an anticipated output (often referred to as the test “signature”), this indicates presence of a defect. The integrated circuit may, in response to such a defect, operate in a reduced function mode and signal an error. If the test is passed, the integrated circuit then automatically transitions into the functional mode of operation.
A common example of this for the automotive industry would apply to the integrated circuit for an electronically controlled braking system. The LBIST would be actuated each time the vehicle is turned on, and further perhaps on a periodic basis during operation, to test the logic functionality for stuck-at and at-speed faults. If the testing is passed, the electronically controlled braking system is configured for full operation. However, if the testing is not passed, a warning signal for brake system failure is passed to the driver.
It has proven difficult to meet customer coverage requirements with the use of pseudo-random patterns for testing. It is also noted that increasing the LBIST pattern count will result in a delay with respect to the integrated circuit passing into the function mode of operation. There is accordingly a need in the art to address the foregoing problems while supporting an LBIST solution for integrated circuit testing.